This invention relates generally to an apparatus and method for depositing one or more materials onto a substrate and in particular to an apparatus and method for depositing one or more materials onto a substrate with one or more composition gradients.
Combinatorial material science refers generally to methods for creating a collection of chemically diverse compounds or materials and to methods for rapidly testing or screening this library of compounds or materials for desirable characteristics or properties. The combinatorial technique, which was introduced to the pharmaceutical industry in the late 1980s, has dramatically increased the drug discovery process. Recently, combinatorial techniques have been applied to the synthesis of organic and inorganic materials. Using various surface deposition techniques, masking strategies or processing conditions, it is possible to generate hundreds or thousands of materials with distinct compositions per square inch in an array of elements which form a library. The materials generated using these combinatorial techniques have included high temperature superconductors, magnetoresistors, phosphors and pigments. The discovery of new catalysts should also benefit from these combinatorial techniques. General combinatorial material science methodologies are disclosed, for example, in U.S. Pat. No. 5,776,359 which is incorporated herein by reference.
Using these combinatorial material science techniques, a substrate, such as a silicon wafer, may have an array of one or more discrete elements formed on the surface of the substrate to form a library of elements. Typically, each element in the library has a slightly different chemical composition so that the library represents a variety of new resulting materials which each may then be tested and characterized to identify new materials with novel chemical and/or physical properties. To form each element, it is necessary to deposit one or more target materials in predetermined amounts into predetermined locations. It is desirable to be able to deposit the one or more target materials in varying amounts for the entire library using a single deposition process. To form such libraries, a predetermined gradient of a target material may be formed across the substrate so that the concentration of the target material may, for example, start at a minimum value at one side of the substrate and increase up to a maximum value at the other side of the substrate. Similarly, a gradient of a second target material may be deposited so that the minimum value is, for example, at the side of the substrate with the maximum amount of the first target material so that a variety of different resulting materials with different compositions of the two target materials are formed on the substrate.
FIGS. 1a, 1b and 1c are diagrams illustrating a conventional apparatus 20 for co-depositing target materials onto a substrate 22. FIG. 1b is a graph illustrating the deposition profiles for the target materials deposited by the conventional apparatus and FIG. 1c shows an extension of the conventional method. In the example of this conventional apparatus shown, two materials, A and B, are going to be co-deposited onto the substrate 22. This conventional method and apparatus are described in an article, Joseph J. Hanak, Journal of Materials Science, Vol. 5 (1970) pgs. 964-971.
FIG. 1a is taken from the above-mentioned publication and illustrates the method. In this method, the target is called a composite target since it is composed of more than one section of different target materials (i.e., target material A 24 and target material B 26). The substrate 22 is of strip shape in order to capture the composition variations along the x-axis. The theoretical composition distribution is shown in FIG. 1b. Using this method, it is easy to see that the various target materials 24, 26 are simultaneously deposited onto the substrate in one deposition process so that they are homogeneously mixed with each other. This is one of the major advantages of Hanak""s method. It is also easy to see that once the composite target is made, the distribution is, to large extent, fixed and cannot be altered easily. This is one of the major disadvantages of Hanak""s method. Alterations of the composition distribution of a given composite target can still be achieved by varying the distance between the target and the substrate and/or locate the substrate at different positions along the x-axis. However, the resulting range of alterations is very limited. In addition, different target materials have different deposition rates if all other conditions are kept the same. Thus, the theoretical distribution of FIG. 1b is usually not realizable (except coincidentally) and therefore Hanak""s method is mainly applicable to those target materials having comparable deposition rates. This is another major drawback of Hanak""s method. From FIG. 1b, it is also evident that, due to the peak and tail of a component profile (an intrinsic property of the distribution), it is difficult to obtain a library element having such a composition that component A is much greater than component B or vise visa. This is another disadvantage of the method.
Using this same method, target materials may be deposited from a 3-component composite target. Another twist of the multi-component composite target co-deposition scheme is when islands of different target materials are placed on the main target as shown in FIG. 1c and described in an article by J. J. Hanak et al, Journal of Applied Physics, Vol. 43(4) (1972) 1666-1673. This scheme is usefull when target materials B and C are intended to be used as dopant materials or the like, since target material A will be the dominant constituents in the libraries made by such a composite target. This scheme can be trivially extended to more dopant component situations. However, the advantages and disadvantages of the method remain the same. The method is also described in U.S. Pat. No. 3,803,438 which is incorporated herein by reference.
Another technique for forming the combinatorial library using deposition techniques is disclosed in an article entitled, xe2x80x9cA Combinatorial Approach to Materials Discoveryxe2x80x9d by X.-D. Xiang et al., published in Volume 268 of Science on Jun. 23, 1995. In this technique, one or more binary masks are used to create the library. As an example, a first mask which divides the substrate vertically in half is used to deposit target material on a left half of the substrate and then a second mask which divides the substrate horizontally in half is used to deposit target material on a top half of the substrate. A third mask may further divide the substrate into four vertical stripes so that a target material may be deposited in two vertical stripes, and so on. In this manner, a library with an array of elements wherein the resulting material in each element may have a different composition of target materials is formed. In particular, layers of the different target materials may be formed and then the layers may be melted together to form the resulting material. These binary masks may be changed so that the composition of the resulting materials in elements in the library may be altered. The problem with this technique is that the various target materials comprising a particular element in the library are formed in layers so that, without further processing such as heating, the various materials are not homogeneously mixed which is undesirable. Although possible, it is very difficult and inefficient to form component gradients in a library by a series of binary masks.
Another technique is described in U.S. patent application Ser. No. 08/841,423, filed on Apr. 22, 1997 and published PCT Application No. WO 98/47613 (based on International PCT Patent Application No. PCT/US98/07799 filed Apr. 20, 1998) which are assigned to the assignee of the present application and which are both incorporated herein by reference. This technique uses a pair of programmable shutter masks to generate the various masking patterns dynamically so that the system is very flexible. This technique, however, still suffers from the drawbacks of the prior technique in that the materials are not homogeneously mixed at the atomic level without further processing, such as heating. A technique of using these mechanical shutters is also disclosed in an IBM Technical Disclosure Bulletin by E. M. DiSilva et al., IBM Technical Disclosure Bulletin, Vol. 22(7) (1979) 2922.
It is desirable to provide an apparatus and method for simultaneously forming a library with gradients of one or more different target materials. The target materials in the library may be homogeneously mixed during the synthesis of the library so that additional processing is not necessary. The target materials in the library may be formed with gradients and the percentage of each target material in each element in the library is programmable and precisely controlled. Thus, it is desirable to provide a programmable flux gradient apparatus for the co-deposition of materials onto a substrate which solves the above problems and drawbacks with the conventional apparatus and methods and it is to this end that the present invention is directed.
A co-deposition apparatus and method are provided which may deposit programmable gradients for two or more target materials onto a substrate simultaneously. The apparatus may also homogeneously mix the two or more target materials at an atomic level since the target materials are simultaneously deposited onto the substrate. The apparatus also permits the gradients for each target material to be independently adjustable and programmable. A method for generating an element in a library with two or more target materials having gradients is accomplished with the co-deposition apparatus in accordance with the invention.
The apparatus may include two or more target material sources from which the target material is ejected onto the substrate. The apparatus may be used with sources which are in line-of-sight with the substrate, such as a thermal evaporator, an electron beam evaporator or a very low pressure sputtering source. The apparatus may be used to deposit two different target materials having possibly different gradients, but may also be used to simultaneously deposit more than two different target materials with possibly different gradients onto a substrate. To control the gradients of the target material ejected by the target material sources, the apparatus may include a programmable gradient shutter associated with each target material source so that each gradient shutter associated with each target material source may control the amount of target material deposited on a predefined region of the substrate. The gradient shutters in the apparatus may be computer controlled.
Thus, in accordance with the invention, an apparatus for simultaneously depositing gradients components of two or more target materials onto a substrate is provided. The apparatus comprises a first target material source that directs a first target material towards the substrate and a second target material source that directs a second material towards the substrate. The apparatus further comprises a gradient mask system that controls a first predetermined amount of the first target material and a second predetermined amount of the second target material directed towards the substrate in order to generate gradients of the first and second target materials on the substrate. The gradients of the first and second target materials being simultaneously deposited onto the substrate form a homogenous resulting material. A method for simultaneously depositing gradients of two or more target materials onto a substrate is also provided.
In accordance with another aspect of the invention, a method for forming a region of a library on a substrate is provided in which the region of the library has a resulting material deposited in the region composed of two target materials. The method comprises simultaneously emitting a first target material from a first target material source and a second target material from a second target material source towards the substrate and controlling a first predetermined gradient of the first target material and a second predetermined gradient of the second target material directed towards the substrate in order to form the resulting material having a first predetermined gradient of the first target material and a second predetermined gradient of second target material. The first and second target materials being simultaneously deposited onto the substrate form a homogenous resulting material.